1. Field of the Invention
This invention relates to an indicating instrument, and more particularly to an indicating instrument for a vehicle or the like in which a pointer indicating driving condition such as vehicle speed and rotation speed of an engine is formed by light, and an indicating instrument system having the above indicating instruments.
2. Description of the Prior Art
FIG. 14 is a schematic drawing showing a cross-sectional view of the structure of a conventional indicating instrument, which is disclosed in Japanese Patent Publication No. Showa 63-193012.
In the figure, denoted 1 is an instrument case, 2a dial having a shape of a flat plate attached to the case 1. On the front surface of the dial 2 is disposed graduations including characters corresponding to the graduations and a hole 2a through which a shaft portion 3a of a rotating body 3 described below is inserted.
Reference numeral 3 shows the rotating body, which comprises the shaft portion 3a inserted into the hole 2a of the dial 2 and top portion 3b engaged with the dial 2. The shaft portion 3a is provided with a center hole 3a1 along an axis thereof and a helical gear portion 3a2 on the periphery of the shaft portion 3a.
Further, the top portion 3b is provided with an opening 3b1 on a periphery thereof.
Denoted 4 is a mechanism mounted on the case 1. The mechanism 4 has a structure of a known analog meter, but, the dimensions thereof are miniaturized.
Reference numeral 4a is a rotation shaft of the mechanism 4, and 5 is a helical gear fixed to the rotation shaft 4a of the mechanism 4. The helical gear 5 engages the helical gear portion 3a2 of the rotating body 3.
Numeral 6 is a point light source emitting a beam B with a round cross section.
Designated 7 is a first reflecting plate disposed on the case 1, which reflects the beam B from the point light source 6 to the center hole 3a1 of the rotating body 3.
Numeral 8 shows a second reflecting plate disposed in the top portion 3b of the rotating body, which reflects the beam B from the center hole 3a1.
Denoted 9 is a cylindrical lens provided in the top portion 3b of the rotating body 3, which converts the shape of the beam into a shape of a line to introduce the beam B on the front face of the dial 2 through the opening 3b1.
Reference symbol P is an optical pointer formed on the front face of the dial 2.
FIG. 15 shows the principle of the conversion from the beam having a round cross section to the linear beam.
FIG. 16 is a drawing for explaining the condition for how the beam is reflected.
In the figure, designated E is the view point from which the indicating instrument is observed.
Next, the operation of the indicating instrument will be explained.
At first, the point light source 6 emits the beam B having a round cross section and the beam B from the point light source 6 is reflected by the first reflecting plate 7 toward the center hole 3a1 of the rotating body 3 and is further reflected by the second reflecting plate 8 toward the cylindrical lens 9.
Then, as shown in FIG. 15, the cylindrical lens 9 converts the round cross section of the beam from the second reflecting plate 8 to a substantially linear or elliptical shape so as to emit the beam B as the optical pointer P.
As described above, light forming the optical pointer P is reflected on the front surface of the dial 2 as shown in FIG. 16, so that the optical pointer P is recognized from the view point E as a pointer.
In the above condition, the rotating body 3 is rotated by the mechanism 4, which provides information on the driving condition through the graduations of the dial 2 corresponding to portions indicated by the optical pointer P. As a result, a driver can recognize the driving condition through reading the graduations on the dial 2 which is pointed by the optical pointer P.
FIG. 17 is a schematic drawing showing a cross-sectional view of the structure of another conventional indicating instrument, which is disclosed in Japanese Patent Publication No. Showa 63-193012. In the figure, like reference characters designate like corresponding parts of FIG. 14 and the explanation thereof will be omitted.
In FIG. 17, 7A is a first reflecting plate, 8A a second reflecting plate attached to a rotation shaft 4a of a mechanism 4.
Numeral 10 shows a housing having a hole 10a through which a beam B from a point light source not shown passes and reaches the first reflection plate 8A.
Denoted 11 is a cap and on a surface thereof opposite to the dial 2 is mounted the first reflecting plate 7A. The cap 11 functions as a cover of the first and second reflecting plates 7A and 8A so as not to be recognized from outside.
The operation of the indicating instrument described above is the same as that of the first conventional instrument. Therefore, the explanation thereof will be omitted.
Meanwhile, in the above publication, another embodiment is disclosed in which the beam from the point light source is introduced into the first reflecting plate or the second reflecting plate through a optical fiber not shown.
With the conventional indicating instrument with the structure described above, the beam B falls on the dial 2 is mostly reflected as shown in FIG. 16. That is, the beam B is mostly reflected in front of the dial 2 in the direction other than the view point E from which the dial 2 is observed.
Therefore, the optical pointer P indicating the graduations of the dial 2 is not recognized clearly, which reduces recognizability of the optical pointer P. In order to improve the recognizability of the optical pointer P, the intensity of the beam B should be increased. However, this causes power consumption to be increased.
With the conventional indicating instrument with the structure described above, one point light source 6 is required for one indicating instrument. Therefore, when a plurality of indicating instruments are used for displaying several types of information on the driving condition such as the vehicle speed, the rotation speed of an engine, the remaining fuel quantity, and the temperature of cooling water for the engine, the measuring system becomes expensive because a point light source 6 with an expensive semiconductor laser or the like is required for each indicating instrument.